1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method for repairing the same, and more particularly, to an LCD device in which a hot pixel is repaired into a dead pixel, and a method for repairing the same.
2. Background of the Invention
Flat display devices including a Liquid Crystal Display (LCD) device, a Plasma Display Panel (PDP), an Electro Luminescent Display (ELD), a Vacuum Fluorescent Display (VFD), etc. have been proposed. Among such flat display devices, the LCD device is being most widely used due to its advantages such as an excellent picture quality, a light weight, a thin profile, and low power consumption. The LCD device is used in various electronic products such as a computer and a television.
In more detail, the LCD device includes first and second substrates facing each other, a switching device formed at the first substrate, an LC layer disposed between the first and second substrates, a pixel electrode, a common electrode, etc. The switching device selectively transmits a voltage from an external driving circuit to the pixel electrode so as to drive the LC layer. As the LC layer is driven by an electric field formed by the pixel electrode and the common electrode, an image can be displayed.
However, the LCD device has the following problems. That is, if source and drain electrodes of the switching device are not normally patterned when forming the switching device, the source and drain electrodes may not be separated from each other. Further, a thin film transistor (TFT) may not be normally driven due to conductive foreign materials remaining at an LC panel, resulting in a hot pixel or a dead pixel.
Also, when implementing a high grey (white state), a ‘dead pixel’ refers to a phenomenon that a region is viewed as a dark region due to light leakage. On the other hand, when implementing a low grey (black state), a ‘hot pixel’ refers to a phenomenon that a region is viewed as a bright region due to light leakage.
FIG. 1 is a schematic view of a related art LCD device. Referring to FIG. 1, pixels (P) include normal pixels (N) and a hot pixel (H). In a black state, the normal pixels (N) are implemented in a dark color, whereas the hot pixel (H) is implemented in a bright color.
Generally, a human's eyes more sensitively recognize a hot pixel (H) implemented in a dark state, than a dead pixel implemented in a bright state. Accordingly, whether an LC panel is good or bad is generally determined based on an inferior state of the hot pixel (H) than the dead pixel. In this instance, the hot pixel (H) is repaired by performing a rework process with respect to a corresponding pixel, or by converting the hot pixel into a dead pixel.
However, in the rework process, the switching device may not be normally driven due to foreign materials remaining thereon. Furthermore, if the first and second substrates are attached to each other when foreign materials remain on the switching device, a rework process cannot be performed.
Therefore, a method for converting a hot pixel into a dead pixel is primarily used. In particular, FIG. 2 is a view showing a repaired pixel in an LCD device in accordance with the related art. That is, FIG. 2 illustrates a Fringe Field Switching (FFS) type LCD device, in which a repair process has been performed in regions ‘a’ and ‘b’.
In the region ‘a’, a repair process is performed so that part of a drain electrode 42 can be cut. Since the drain electrode 42 is provided with a voltage from a source electrode 41 by a channel of an active layer 30, the voltage is not applied to a pixel electrode 15 connected to the cut drain electrode 42. That is, the pixel electrode 15 is floating. However, a potential of the floating pixel electrode 15 is different from a common electrode 60. This causes a corresponding pixel to operate as a hot pixel. Accordingly, a repair process is performed with respect to the region ‘b’.
In the region ‘b’, a repair process is performed so that the pixel electrode 15 and the common electrode 60 are electrically shorted to each other. FIG. 3 illustrates a section of a pixel repaired in the region ‘b’. Referring to FIG. 3, the repair process in the region ‘b’ is performed by welding an upper part of the common electrode 60 so as to form a passage connected to the pixel electrode 15 from a lower part of the common electrode 60.
As the passage is formed, the pixel electrode 15 and the common electrode 60 come in contact with each other. As the pixel electrode 15 and the common electrode 60 are electrically connected to each other, there is no potential difference therebetween.
In addition, because the repaired pixel electrode 15 has no potential difference from the common electrode 60, a horizontal electric field is not formed. Accordingly, an aligned state of LC molecules corresponding to the repaired pixel is not changed. That is, the repaired pixel is observed as a dead pixel in a black state.
If the LCD device is immediately driven after the repair process, the repaired pixel is observed as a dead pixel. However, the repaired pixel may be observed as a hot pixel, as the passage for connecting the pixel electrode 15 and the common electrode 60 to each other is closed by a voltage or heat generated from the repaired pixel, after the LCD device is continuously driven.
Furthermore, the repair process has a difficulty in passing through a thick film including a passivation layer and a gate insulating film each disposed between the pixel electrode 15 and the common electrode 60. It is also difficult to perform a welding process with respect to the pixel electrode 15 and the common electrode 60 each formed of a thin film having a thickness of 300 Å˜400 Å.